1. Field of the Invention
The present invention relates generally to Global Positioning System (GPS) receivers, and in particular, to a GPS receiver with a Pseudo Noise (PN) code output.
2. Description of the Related Art
The use of GPS in consumer products has become commonplace. Hand-held devices used for mountaineering, automobile navigation systems, and GPS for use with cellular telephones are just a few examples of consumer products using GPS technology.
GPS-enabled devices, such as cellular telephones, have also been introduced into the consumer marketplace. These devices allow for the use of Location-Based Services (LBS) which are services, advertisements, and other features that are offered based on the location of the user. As such, GPS-enabled devices are used worldwide.
One of the problems with GPS-enabled devices when used for LBS, or for Emergency 911 (E911) calls is that GPS signals do not have the signal strength necessary to be usefully received when the GPS satellites are not visible in a line-of-sight fashion. So, for example, when a GPS-enabled cellular telephone is inside of a building, parking structure, etc., the GPS positioning functions of that cellular telephone are limited if not completely disabled.
Much of the focus for LBS and E911 has been to determine how best to get cellular telephones to be able to determine position when GPS satellites are not in direct view. Aiding of the GPS signal through the cellular system has provided some help, but most cellular telephones need more than just a time base to determine their position; the addition of a guaranteed time only removes one variable from the equations that must be solved by the GPS receiver.
It can be seen, then, that there is a need in the art to make GPS-enabled devices operable in environments where GPS satellites are not directly visible.